This article is outdated. For the Game Patch 1.2 updated article about PvP gear, please click here.
[UPDATED at Patch 1.1.5]
I've noticed that most of the players don't know how to get their PvP gear, so I'll try to explain it as clearly as possible.
There are 3 epic PvP gear sets (by rate): Centurion
. There are 2 and 4 piece bonuses for all of them which you can get even if you mix Centurion with Champion gear for example.
The PvP vendors can be found on the Republic Fleet/Imperial Fleet in the Combat Training sector, same as the terminal which gives PvP dailies/weeklies.